Well my two cents: if you have the budget, would be to build the bay window section out to level with the adjoining section. the resulting overhang would still break your façade and give it new interest.
The windows i suggest : http://www.deco.fr/diaporama/photo-des-fenetres-de-style-atelier-11270/ You can see the possible variations in the slide show, sorry it's in french but i don't know the term in english. This style is fast gaining popularity in France for exterior and interior solutions.
They can still work well if you just replace the bay with them, but they should be set inwards as far as possible. Another important point, the existing windows are placed far too high, almost touching the gutter, very wrong shui and displeasing.
Now, if we're looking at a double room here and you build out the front as i suggest then you can run the windows the whole length, which would look very dramatic.
Otherwise if the front remains the same then as well as lowering you should narrow slightly, windows right on the edge like this is more very wrong shui.
Of course, the rest of the windows would need to follow this style, and you need to call in a pro who can produce you a mock up and help you get the balance and proportion just right.
Otherwise, plain big sliding glass panels would look very good as well, darker frames as you say and as slim as possible.
I shall put my thinking cap on for the rest, also to avoid a TLDR post.

Thanks so much for your great idea of building out the front. That's why this community is so good. I hadn't thought of that. Interesting windows. I do understand some French :-) The room with bay window will be through family living space, open plan to kitchen and dining room to rear. Room adjoining is larger separate living area. Yes I agree the proportions are all wrong. The windows we are looking at are German, but I think they can pretty much give us whatever profile we want. Also to consider is that this is a very sunny facade. Appreciate your thoughts a lot.

This is why it's always good to have a pro to hold your hand for at least some of the way, (carefully chosen though, check out his/her finished projects, the more varied the styles, the better she/he will be able to understand and adapt to your desires), they can provide the invaluable visual supports too.
When it's your own house it's notoriously difficult to see the possibilities, you have it under your eyes the whole time and the defaults shout at you and prevent you being able to see it objectively and envisage the possibilities. you're emotionally involved and emotions always have the upper hand on the brain, so you just keep turning round in circles.
Something akin as to why a psy must never attempt therapy on a member of his own family, if you follow me :D

As for the façade color, are you sure it needs changing that much ?
Once those thick white frames have gone and the new windows nestling more discreetly, correctly positioned and re-proportioned, the aspect will change drastically and be far more streamlined and modern. (the devil is in the detail)
I'd also strongly suggest that the wood facing just breaks off around the windows, no framing or finishings. Same thing for all the windows, the small ones too.

Entrance : Same as for the windows, that outer frame shouldn't be touching the ceiling, you can try taking that off and painting the door another color before deciding to change it and once again the door could do with setting back a little. You could maybe take that doorstep out while you're at it.
Also, i don't know what is happening to the right of the door but i see the concrete steps leaing up and feel it would be good to create another level to make it flush with the bottom of the door if structurally possible. This would tie it all in better and you probably wouldn't need any additional definition to your entrance.
Anyhow, as i often quote, i'm a firm believer in " Less is More " , and vice versa of course ^^

Question #4 i can't answer as i haven't really understood the problem
And #5 i don't think so, but once the other transformations have been taken care of i think you'll find it speaks for itself.

Whatever, it's a very exciting project, the bones are great and i'd love to see photos of progression once you get started.